Research On Performance Of Axial Flow Pump In Saddle Area

This work was funded by the Results Transformation of Special funds of Jiangsu Province(Grant BA2013127)and Production and Research Joint Innovation Funds Program of Jiangsu Province(Grant BY2014123-07).Axial flow pumps is low-lift pump,which is widely used in agricultural irrigation and drainage,water environment management,urban water supply engineering and ecological water demand engineering.The stability of the axial flow pump has always been a hot topic in the field of hydraulic machinery.Saddle area characteristics of H-Q curve influence the running stability of the axial flow pump,especially the stability during start and stop process.Therefore,it is very important to study the running characteristics of the axial pump in the saddle area.In this paper,an axial flow pump which ns is 822 was studied.The numerical simulation and experiment approachs was used to study the characteristics of the internal flow,energy,pressure pulsation and vibration at different conditions.The running characterics analysis of axial flow pump in saddle area were focused.1.The significance of the study on the running characteristics of axial flow pump in saddle area was introduced.The research status of the inner flow field,pressure pulsation characteristics and vibration characteristics of the axial flow pump were systematically analyzed.2.An axial flow pump test rig was set up to study energy characteristics,pressure pulsation characteristics and vibration characteristics of the pump.The operation characteristics of the axial flow pump in the saddle area were analyzed.The experiment results show that(1)saddle area is located within 0.5QBEP~0.6QBEP and the head at 0.55 QBEP is smallest in saddle area.(2)The pressure pulsation amplitude of impeller inlet is higher than that of other three measuring points.The maximum pressure pulsation in the saddle area is located at the impeller inlet of 0.55 QBEP,when the peak peak value of pressure pulsation is 2.3 times than that of the best effciency condition.The main frequency of impeller inlet at each condition is f_p.(3)The main frequency of the vibration spectrum is fn.The vibration level in the vertical direction of the impeller inlet and outlet is the largest.In impeller inlet vertical direction,the vibration velocity at f_p under 0.6QBEP is 1.15 times than optimal condition,the vibration velocity at f_p under 0.55 QBEP is 1.05 times than optimal condition;In impeller outlet vertical direction,the vibration velocity at f_p under 0.6QBEP is 1.1 times than optimal condition,the vibration velocity at f_p under 0.55 QBEP is 1.04 times than optimal condition.3.The CFD method was used to simulate the inner flow field of axial flow pump.The static pressure,blade vorticity,impeller flow line and impeller equivalent stress were analyzed.The results show that(1)under the optimal conditions,the static pressure distribution on the blade surface is uniform.The suction surface of the blade has a large low pressure area in saddle area.(2)Under the optimal condition,the velocity helicity Hn on blade pressure surface and suction surface is uniform distributed.The Hn has a significant concentrated area and the pressure pulsation in the saddle area is enhanced because of the existing of eddy.(3)Under the optimal condition,the impeller streamline distribution is more uniform and more regular.In saddle area,the backflow exists at the impeller inlet near the front edge and eddy exists at impeller outlet near the hub,that make the flow of the pump more disorderly.4.Based on the experiment,the energy characteristics,pressure pulsation characteristics and vibration characteristics of the axial flow pump with different blade placement angle in saddle area were studied.The results show that(1)the flow,head and efficiency increase gradually when the blade placement angle increases.The flow,head and efficiency increase by 26.7%,10.4% and 0.87 percentage points when the blade placement angle is changed to +4°from-4°.(2)The absolute position of the saddle area is shifted to the upper right,but the relative position is still mainly located in 0.5QBEP~0.6QBEP with the increase of blade placement angle.(3)The pressure pulsation peak peak value at impeller inlet increases gradually with the increase of blade placement angle and the pressure pulsation peak peak value at +4° under 0.55 QBEP is 1.22 times than that of 0°.(4)The main frequency of pressure pulsation at impeller inlet is f_p at each conditions.The pressure pulsation amplitude at +4° under 0.6QBEP is 1.26 times than that of 0°(5)The vibration level increases gradually with the increase of blade placement angle.In impeller inlet vertical direction,the vibration level at +4° under 0.6QBEP is 1.01 times than that of 0°.In impeller outlet vertical direction,the vibration level at +4° under 0.6QBEP is 1.03 times than that of 0°.5.Based on the experiment,the energy characteristics,pressure pulsation characteristics and vibration characteristics of the axial flow pump with 60°outlet elbow were studied.The running characteristics were compared with that of 90°outlet elbow.The results show that compared with 90°outlet elbow,(1)the flow,head and efficiency increase by 3.1%,3.5% and 2.02 percentage points when the outlet elbow is 60°.(2)The absolute position of the saddle area is shifted to the upper right,but the relative position is still mainly located in 0.5QBEP~0.6QBEP when the outlet elbow is 60°.(3)The vibration level decreases when the outlet elbow is changed into 60° from 90°.In impeller inlet vertical direction,the vibration level under 0.6QBEP deareases by 0.19%,the vibration level under 0.55 QBEP deareases by 1.13%.In impeller outlet vertical direction,the vibration level under 0.6QBEP deareases by 0.2%,the vibration level under 0.55 QBEP deareases by 0.27%.